Design and fabrication of subwavelength annular aperture and its application to laser machining
Date Issued
2010
Date
2010
Author(s)
Yu, Yuh-Yan
Abstract
Traditional optical systems are affected by diffraction limit such that its focal spot size is limited by the incident wavelength and numerical aperture of the system. In order to shrink the focal spot, two common methods are typically used. One method is to reduce the wavelength of the light source, and another is to increase the numerical aperture of the lens. However, the high cost of light source and the rarity of lens material at shorter wavelength obstruct the development of lithography techniques.
In recent years, the fabrication and design of subwavelength annular aperture (SAA) structure have been developed well. In this thesis, we used the principle of surface plasmon to design and fabricate the SAA structure. We proposed silver and Al2O3-Al-Al2O3 SAA structures. Utilizing these nontraditional phenomena, the SAA structure possesses both ultra-long depth of focus (DOF) and a few hundreds of nanometer spot size simultaneously. We also established a Bessel beam writer system which is integrated with SAA structure and high energy laser system such as femtosecond or Excimer laser.
For the simulations part, we demonstrated the far-field optical properties of different polarization and different light source of metallic SAA structure by using three-dimensional FDTD simulations. We also compared the optical transmission results of a metallic SAA structure with different polarization and light source.
For the experimental parts, we demonstrated a new technique which uses electron beam lithography (EBL) for pattern generation followed by a metal lift-off process to fabricate a large size SAA structure on metallic film deposited on top of a glass substrate. We can see that by adopting this technique, we can significantly extend the DOF by increasing the diameter of the SAA structure. In practical applications, we demonstrated a new technique which focuses a Ti:sapphire femtosecond and Excimer laser onto an oxide-metal-oxide (Al2O3/Al/Al2O3) film on a glass substrate engraved with a SAA structure. We found that SAA structure is one of the best choices to develop a Bessel beam writer system prototype that can produce high aspect ratio laser-machining easily and conveniently within an atmospheric environment in the future.
Subjects
Optical lithography
Surface plasmon
Subwavelength annular aperture
Bessel beam
Laser-machining
Type
thesis
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